We report here the measurements of vibrational excitation spectra and the temperature dependence of (Formula presented) molecules adsorbed on Si(111)-(Formula presented) and Si(100)-(Formula presented) surfaces using high-resolution electron-energy-loss spectroscopy in combination with scanning tunneling microscopy. A quantitative determination of the molecular charge state is obtained by the lower energy shifts of vibrational modes of (Formula presented) upon adsorption. On the Si(111)-(Formula presented) surface, the amount of charge transfer from the surface to a (Formula presented) molecule is estimated to be (Formula presented) electrons at the coverage lower than 0.25 monolayer (ML) and (Formula presented) electrons as an average at 1 ML. On the contrary, no indication of charge transfer is observed on the Si(100)-(Formula presented) surface at a coverage lower than 1 ML. The difference in the charge state on both surfaces is attributed to the difference in the nature of surface states. After annealing 1 ML (Formula presented) film at 500 K, the strong interaction between the surface Si atom and a (Formula presented) molecule is indicated by the softening of vibrational modes on both surfaces.
|ジャーナル||Physical Review B - Condensed Matter and Materials Physics|
|出版ステータス||Published - 1997 1 1|
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